Devices which employ a thin, elongated dipstick for measuring the oil level in a crankcase of an internal combustion engine are generally well known. See, for example, Jansch U.S. Pat. No. 4 640 126, issued Feb. 3, 1987; Braun U.S. Pat. No. 3,474, 884 issued Oct. 28, 1969; and Suhr U.S. Pat. No. 4,894,926, issued Jan. 23, 1990.
Such devices typically include an oil dipstick tube extending from the oil crankcase to the exterior of the engine. A dipstick is configured for sliding receipt within the dipstick tube such that a distal end of the dipstick extends into the crankcase when the dipstick is seated in the dipstick tube.
To aid the operator in aligning the distal end of the dipstick with the open end of the dipstick tube into which the dipstick is to be inserted, some presently known devices provide a dipstick tube having a flared end portion which diverges outwardly, forming an enlarged open end, the inside surface of the enlarged portion being continuous with the inside diameter of the rest of the dipstick tube. Once the distal end of the dipstick is positioned within the enlarged portion of the dipstick tube, the dipstick may be easily guided along the inside surface of the enlarged portion and into the dipstick tube.
For example, Delano U.S. Pat. No. 4,155,167, issued May 22, 1979, discloses a guide element which is urged downwardly against a biasing spring, such that the dipstick tube extends above the guide element when the dipstick is seated within the dipstick tube. When the dipstick is removed from the tube, however, the guide element forms a continuous surface with the inside diameter of the dipstick tube, i.e., the dipstick tube does not remain extended above the upper surface of the guide element. Impurities such as dirt, dust and the like which collect on the upper surface of the guide element can enter the crankcase through the dipstick tube.